Drought stress inhibits seed germination of alfalfa （Medicago sativa L.） and reduces its yield. This research studied the effects of cerium oxide nanoparticle priming on seed germination and physiological characteristics of alfalfa under drought stress. Alfalfa seeds were used as materials and primed with different concentrations of cerium oxide nanoparticle （CeO₂NPs） solutions （0， 50， 100， 150， 200 mg·L^-1） in the dark for 24 hours. Drought stress was simulated with 15% PEG to explore the mitigating effect of CeO₂NPs on seed germination. The results showed that 15% PEG significantly inhibited seed germination， while priming with 150 mg·L^-1 CeO₂NPs increased the germination rate to 77% （P<0.05）， which was 5% higher than the non-primed treatment. It also shortened the average germination time， increased the germination index， and enhanced the fresh weight of germinated seedlings. At the physiological level， the 150 mg·L^-1 CeO₂NPs priming treatment increased the activities of α-amylase and β-amylase， and significantly reduced the contents of reducing sugar （P<0.05）； the 100 mg·L^-1 treatment significantly improved the activity of antioxidant enzymes； the 50 mg·L^-1 treatment effectively reduced the ROS content； all concentrations of CeO₂NPs priming treatments significantly decreased the malondialdehyde content （P<0.05） and the proline content， and increased the soluble protein content as osmotic adjustment substances. Comprehensive analysis indicated that 150 mg·L^-1 CeO₂NPs priming had the best mitigating effect on alfalfa seed germination under drought stress.

Alfalfa  /  Drought stress  /  Cerium Oxide Nanoparticles  /  Seed priming  /  Seed germination